Nielsen Mobile (press release): "Nielsen Mobile, a service of The Nielsen Company, estimates that 2.9 million US mobile subscribers received a text message from the Obama campaign over the course of Friday, Saturday and Sunday.

How does Nielsen know this? Nielsen Mobile monitors shortcode marketing (the use of text-message shortcodes such as the 62262 “O-B-A-M-A”) through the world’s largest telecommunications bill-panel, an opt-in panel that reports on the billing activity for more than 40,000 subscriber lines in the US. It’s just one of the many ways Nielsen reports on wireless and mobile media consumers."